It is well known to attach a variety of rigs such as hydraulically operated rigs above a wellhead. For example, snubbing units are known in the oil and gas industry for facilitating access to a well which is under pressure including, for example, well operations such as well completions. A snubbing unit includes structure and equipment above a wellhead for manipulating tubular components such as pipe, tubing, and bottom hole assemblies (BHA) in and out of a well while controlling the well under pressure.
Generally, a snubbing unit employs stationary (lower) and traveling (upper) slip assemblies, opposingly oriented, to releasably and controllably shift tubular components into and out of the well through a wellhead despite the possibility of either heavy tubular loads, which urge the tubular components to fall into the well, or the pressure-generated forces on the tubular components, which urge the tubular components out of the well. The snubbing unit is installed above an existing wellhead seal, such as that created by a blow-out preventer (BOP), and incorporates its own seals to seal the tubular components as they are introduced or removed from the wellhead, such as through the use of a stripping head.
Most conventional snubbing units fall into either rig-assisted or self-contained units. Rig-assisted snubbing units are typically snubbing units that are pivotally mounted to a truck and require assistance by an onsite service rig so as to winch them upright, pivoting from the truck, to a snubbing position over the wellhead. Self-contained units are typically transported to site on a truck and lifted into position, over the wellhead, by a separate crane unit. During operations, self-contained snubbing units do not require the assistance from an on-site rig.
When snubbing in low-pressure well environments, such as wells with surface pressures under 12,000 kPa, a compact, rig-assisted snubbing unit is often the ideal choice. A compact snubbing unit can be easily transported to the well site, such as in a 1 ton pickup truck, and is practical and cost effective for single wells and underbalanced drilling. Additionally, a compact snubbing unit reduces or eliminates viewing obstructions often experienced by service rig operators when utilizing traditional (larger) sized snubbing units. One example of a compact snubbing unit is the one marketed under the trade-mark MINI BRUTUS by Team Snubbing Services Inc. of Rocky Mountain House, Alberta, Canada.
Despite the many advantages of a compact snubbing unit, the set-up of such a unit still requires the snubbing unit to be installed above an existing wellhead seal and to incorporates its own seals to seal the tubular components as they are introduced or removed from the wellhead. Typically a compact snubbing unit, such as the MINI BRUTUS™, is installed above a blow-out preventer (BOP) and incorporates an RS-100 stripping head as its seal to seal the tubular components.
Push/pull systems or push/pull units are also known in the art and are used to manipulate tubular components in and out of a well. Push/pull units provide alternatives to, and/or improvements over, conventional snubbing systems. Such push/pull systems are generally mounted at the rig floor (e.g. on the rotary table) and, therefore, allow live well operations to be conducted at the rig floor rather than in the greatly elevated work baskets as is generally the case with conventional snubbing units. One example of a push/pull system is that manufactured by Tesco Corporation of Calgary, Alberta, Canada. However, the prior art push/pull systems manufactured by Tesco Corporation is cumbersome, large and heavy, does not have the compactness that has become associated with compact snubbing units such as the MINI BRUTUS™ and cannot be used to retrofit such compact snubbing units and/or convert such units into a push/pull system.
Applicant's prior-filed applications (U.S. Ser. Nos. 61/148,922 and 12/464,034) and issued Canadian patent no. 2,652,068, address many of these above-noted disadvantages, and as more clearly illustrated in FIGS. 1-18 and the following background description thereof.
Referring to FIGS. 1-18, a PRIOR ART compact snubbing or push/pull unit 12 (or most of the components thereof) is supported on a PRIOR ART load bearing apparatus or support structure 20 having a central passage 20c of sufficient diameter to allow passage of tubular components T therethrough, preferably having at least one tensile member mount 21 to facilitate the connection of one or more tensile members 40 between the support structure 20 and a mounting point on a rig or rig floor RF and having a support member or support plate 22. The support plate 22 is adapted to be secured to, or within, the compact snubbing unit 12. The compact snubbing unit 12 comprises stationary (lower) and traveling (upper) slip assemblies 14s, 14t, traveling plate 15t (to support the travelling slip assembly 14t and having a central passage 15tc of sufficient diameter to allow passage of tubular components T therethrough), bottom or stationary plate 15s (to facilitate mounting of the compact snubbing unit 12 to the support structure 20 and having a central passage 15sc of sufficient diameter to allow passage of tubular components T therethrough) and a pair of jacking rams 16a, 16b securely mounted to the stationary plate 15s and actuatable in a conventional manner to releasably and controllably shift tubular components T into and out of the well through a wellhead. Preferably, jacking rams 16a, 16b are hydraulic rams.
Jacking rams 16a, 16b are securely mounted to the compact snubbing unit 12 in the conventional manner. The stationary plate 15s comprises paired ram cut-outs or recesses 15a, 15b, said ram recesses 15a, 15b being substantially positioned at 180° across from each other around central passage 15sc and at the periphery of the stationary plate 15s (see FIG. 12). Further, the jacking rams 16a, 16b each comprise an annular groove 16ag, 16bg of such diameter and dimensions to allow secure placement of the jacking rams 16a, 16b within the ram recesses 15a, 15b (see FIG. 7) and the compact snubbing unit 12 further comprises ram keepers or ram retainers 17a, 17b. As such, jacking rams 16a, 16b are securely mounted to the compact snubbing unit 12 in the conventional manner, i.e. by placing the annular grooves 16ag, 16bg of jacking rams 16a, 16b within the respective ram recesses 15a, 15b and then bolting or otherwise fasten the ram retainers 17a, 17b so as to maintain secure placement of the jacking rams 16a, 16b on the stationary plate 15s (see FIGS. 6-8, 10 and 11).
The support structure 20 further comprises ram openings or ram passages 22a, 22b, in the support plate 22, each ram passage 22a, 22b being coaxially aligned with ram recesses 15a, 15b of the stationary plate 15s and each ram passage 22a, 22b being of sufficient diameter to allow passage of the jacking rams 16a, 16b therethrough (see FIGS. 1, 5-6, 9 and 10). Preferably, ram passages 22a, 22b, while allowing of passage of the jacking rams 16a, 16b therethrough, are positioned and are of such dimensions so as to have the support structure 20 still provide some contact surface area SA or support for the ram retainers 17a, 17b and are not so large so as to also allow passage of said ram retainers 17a, 17b therethrough when the compact snubbing unit 12 is mounted to the support structure 20 and is subject to pushing or pulling forces from the tubular components T. As more clearly shown in FIGS. 1-6, the support structure 20 comprises plurality of rig engaging members or legs 24 distributed around and connected to the support plate 22.
The support plate 22 is secured to the compact snubbing unit 12 by bolting or fastening to the stationary plate 15s in a conventional manner. The stationary slip assembly 14s is unfastened from the stationary plate 15s, stationary plate 15s and ram retainers 17a, 17b are fastened directly underneath the support plate 22 and stationary slip assembly 14s is placed and fastened directly above the support plate 22 thereby sandwiching the support plate 22 between the stationary slip assembly 14 and the stationary plate 15s (see FIGS. 6 and 10). As such, support structure 20 is mounted within the compact snubbing unit 12. In another variation of this PRIOR ART support structure (not shown), the stationary plate 15s is fastened directly on top of and against the top surface of the support plate 22 and then the support structure 20 can more easily accommodate significant downward forces, such as those which might be created when heavy tubular loads urge the tubular components T to fall into the well.
During operations, the support structure 20 is positioned on a rig floor RF above a wellhead (not shown) extending from the ground and including standard wellhead components and wellhead seals. Loads and downward forces from the compact snubbing unit 12 and/or tubular components T are generally distributed into the rig floor RF through the support structure 20 and legs 24. Where upward forces (e.g. where the well pressure-generated forces on the tubular components T urge the tubular components T out of the well) are expected to be incurred, one or more tensile members 40 can be utilized to further secure the support structure 20 to the rig or rig floor RF via the tensile member mounts 21. Typically, tensile members 40 are chains and fasten the support structure 20 to the rig floor RF in a conventional manner.
FIG. 13 illustrates an alternate PRIOR ART variation of a support unit 20, which is similar to that of FIGS. 1-12, but wherein the compact snubbing unit 12 does not comprise a stationary plate, wherein the ram passages 22a, 22b are adapted to act as, and have similar dimension to, the ram recesses 15a, 15b of the embodiment in FIGS. 1-12, and wherein the jacking rams 16a, 16b are securably mounted directly to the support plate 22 of the support structure 20 (in a similar or identical manner as they are mounted to the stationary plate 15s of the embodiment of FIGS. 1-12) through use of ram retainers 17a, 17b. 
FIGS. 14-18 illustrate the configuration of another PRIOR ART variation of a support unit 20 which is similar to that of FIGS. 1-12, but which further comprising a worker platform 50 to support a worker W. The worker platform 50 places a worker W in a safe and efficient position to conduct well operations and to handle the tubular components T.
However, prior to installing a compact snubbing unit or push/pull unit and/or in combination with a support structure 20, tubular components may already be positioned fully through a rig floor, or extend up from the wellhead partway up through the rig floor. For example, when tubular components are stuck in a wellbore, then a snubbing or push/pull unit 12 may be helpful to provide additional force to move and loosen such stuck tubular components T. In such a case, the tubular components T may need to be disconnected and removed; and/or the compact snubbing unit or the push/pull unit 12 may have to be lifted into position, over top of such tubular component T, by a separate crane unit or the like. This complicates installation of the compact snubbing or push/pull unit 12, may require cranes or the like and adds to the installation time and cost of the compact snubbing or push/pull unit 12 onto the rig floor. What is needed is a compact snubbing or push/pull unit and/or support structure 20 that does not suffer from the above-noted disadvantages and which can be easily installed onto a rig floor RF when tubular components T are already present and extend up through the rig floor RF.